For some time, fatty acid polyethylene glycol esters, more particularly fatty acids with a low degree of ethoxylation, such as fatty acid +1EO adducts, have been described in the literature as interesting intermediates for the synthesis of ether sulfate surfactants with an isethionate-like structure. At first, however, difficulties were involved in producing the fatty acid polyethylene glycol esters used as starting compounds in satisfactory selectivities. Apart from the unwanted percentage of relatively highly ethoxylated homologs, significant quantities of polyethylene glycol and diesters were also formed by the relatively old known processes. Only recently has it been possible to produce fatty acids with low degrees of ethoxylation in yields of more than 90% of the theoretical by using special alkanolamines as ethoxylation catalysts. Apart from the fact that it was already difficult enough to provide the starting compounds in suitable qualities, the sulfation of these compounds also presented considerable difficulties. Although, according to the artide by K. Engel and W. Rubak in Fette, Seifen, Anstrichm., 88, 20 (1986), sulfated fatty acid polyethylene glycol esters can be obtained by reacting fatty acid polyglycol esters with chlorosulfonic acid in methylene chloride, only traces of anionic surfactants could be detected after neutralization under standard conditions. In other words, the mixture left after neutralization contained hardly any more anionic sulfated fatty acid polyethylene glycol esters, but mainly hydrolysis products, such as fatty acids, soaps, short-chain glycol monosulfates and glycol disulfates. Better results were obtained when the neutralization step was carried out at temperatures of 0 to -20.degree. C. However, a process such as this would be unsuitable for industrial-scale production because, on the one hand, methylene chloride is used as solvent and would have to be removed in a separate working-up step and, on the other hand, cooling for working temperatures below 0.degree. C. would only be possible on an industrial scale at enormous cost.
Accordingly, the problem addressed by the present invention was to provide an improved process for the sulfation of fatty acids, especially fatty acids with a low degree of alkoxylation, which could be used on an industrial scale to provide fatty acid polyglycol ester sulfates without any further working up.